ABSTRACT Aim: Randomized phase III study for the first-line treatment of advanced gastric cancer (AGC) (G-SOX PIII) demonstrated the non-inferiority of S-1 plus oxaliplatin (SOX) for S-1 plus cisplatin (CS) on PFS (HR for SOX vs. CS 1.004, 95% confidence interval [CI] 0.840-1.199; Higuchi, JCO 2013;30:Suppl, Abstract 60) and on OS (HR 0.958, 95% CI 0.803-1.142). Reporting of separate analyses for individual progression types is recommended (European Medicines Agency. Appendix 1 to the guideline on the evaluation of anticancer medicinal products in man). Thus, we aimed to assess the association between progression types and OS in this study. Methods: Tumor lesions were assessed every 6 weeks until disease progression and independently reviewed according to the RECIST v1.0. We applied the Cox regression including two time-dependent covariates, i.e., progressive disease with new lesions (PDNL) or without new lesions (PDwoNL) in each treatment group, and estimated their effects compared to no progression (Non-PD). Results: The results of analysis are shown in the table below. PDNL and PDwoNL were identified for 88 and 166 patients in SOX group (317 patients), and 95 and 146 patients in CS group (324 patients), respectively. The hazards of death in Non-PD were different between treatment groups (HR 0.582). However, association between progression types and OS were similar in both treatment groups. Both progression types were strong prognostic factors for OS, and greater effects were seen in PDNL (HR 8.277 in SOX, 5.997 in CS). Conclusions: The progression accompanied by new lesions gives a strong negative impact on OS in patients treated with S-1 and platinum for AGC. Examining progression types would be useful for evaluating efficacy of anticancer treatment on OS. HR (95%CI) P SOX vs. CS in Non-PD 0.582 (0.371-0.914) 0.019 in PDwoNL 1.111 (0.868-1.589) 0.403 in PDNL 0.803 (0.593-1.089) 0.158 SOX PDwoNL vs. Non-PD 5.447 (3.609-8.221) PDNL vs. Non-PD 8.277 (4.250-8.462) CS PDwoNL vs. Non-PD 2.854 (2.038-3.995) PDNL vs. Non-PD 5.997 (4.250-8.462) Disclosure: Y. Yamada: honoraria: Yakult Honsha, Taiho, Chugai, Pfizer, Takeda, Bristol-Myers, Dainippon Sumitomo, Johnson & Johnson, Novartis, Daiichi Sankyo Research Funding: Yakult Honsha, Otsuka, Chugai, Pfizer, Astra Zeneca, Novartis, Daiichi Sankyo, Bayer, Merck; K. Higuchi: I have received honoraria from Yakult Honsha; M. Gotoh: I have received honoraria from Yakult Honsha; N. Fuse: I have received honoraria from Taiho and research funding from Yakult Honsha and Taiho. N. Sugimoto: I have received honoraria and research funding from Yakult Honsha and Taiho; T. Nishina: I have received honoraria and research funding from Yakult Honsha and Taiho; A. Tsuji: I have received honoraria from Yakult Honsha and Taiho; K. Yamaguchi: I have received honoraria from Chugai, Bristol-Myers, Takeda, and Merck; H. Yasui: I have received honoraria from Yakult Honsha, Medicon, Chugai, Taiho, and Bristol-Myers. S. Hironaka: I have received honoraria from Yakult Honsha and Taiho; C. Hamada: I have received consultant fees and honoraria from Yakult Honsha, Taiho, and Chugai; I. Hyodo: I have held an advisory Role for Yakult Honsha and Taiho. I have received honoraria from Yakult Honsha and Taiho. All other authors have declared no conflicts of interest.